Bicycle rim structure provided for a tubeless assembly and bicycle wheel

ABSTRACT

A rim structure for a bicycle wheel that includes, at its periphery, an annular channel designed to receive a tire, such channel being demarcated by an upper bridge devoid of openings with the exception of the valve opening, and two lateral flanges, such flanges having end butts for gripping the tire. The upper bridge has a narrow and recessed central rim well demarcated by a base and two lateral walls, the rim well being bordered by two bead seats that are oblique from the rim well towards the flanges. The invention is also related to a wheel having such a rim and a wheel equipped with a tire mounted without an air tube and having such a rim.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/121,704, filed on Jul. 24, 1998, the disclosure of which ishereby incorporated-by-reference thereto in its entirety and thepriority of which is claimed under 35 U.S.C. §120.

[0002] This application is also based upon French Application No. 9709928, filed on Jul. 25, 1997, the disclosure of which is herebyincorporated by reference thereto in its entirety and priority of whichis claimed under 35 U.S.C. §119.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] This invention is related to a rim structure for a bicycle wheel.The invention is also related to a bicycle wheel having such a rim, aswell as to a wheel having such a rim equipped with a tire.

[0005] The invention especially relates to a rim of the butt or hooktype that is designed for a so-called “tubeless” assembly, or in otherwords, without an air tube.

[0006] 2. Description of Background and Relevant Information

[0007] In a known manner, a wheel has a rim and a hub connected to therim via two sets of spokes. The rim generally includes two bridgesconnected to one another by lateral flanks that extend beyond the upperbridge via rim flanges so as to form an annular channel where the tirecan become housed. At their upper portions, the rim flanges have abutt-like or a hooked portion whose function is to retain the tire afterinflation. Normally, the bridges of the rim are bored with openings thatare used for the passage or retention of the spoke nipples.

[0008] Tubeless assemblies for tires are known. Such an assembly isadvantageous because it eliminates the cost, mounting and weight of anair tube. In addition, such an assembly makes the wheel equipped withthe tire less prone to punctures due to pinching or perforation. Athorn, for example, that passes through the tire remains, in effect,embedded in its housing, so that hardly any air, or just a negligibleamount of air, is lost.

[0009] In order to obtain a tubeless assembly of the tire, it has beenknown to block all the openings of the spokes by a sealed rim base. Thepatent application EP 615 865 discloses such a technique. However, it isdifficult to seal all of the spoke openings. In order to remedy this,the above-cited application also proposes that the lips of the tirecover the edges of the rim base, so as to form a closed volume alongwith it. This requires a special type of tire, whose assembly is adelicate operation.

[0010] In order to overcome the sealing problem of the rim, the patentapplication DE 42 06 311 also proposes obtaining a rim whose upperbridge is not bored. The spokes are thus anchored in the openings of thelower bridge. The fact that the upper bridge is smooth, i.e., it has noholes except for the valve opening, resolves sealing problems in thisarea. In addition, such a rim is compatible with conventional tires.However, this solution gives rise to a sealing problem between the sidesof the tire and the rim. The problem becomes apparent when the tire isinflated, especially if the inflation is done with a low output device,such as a manual pump, for example. In fact, when the tire is mounted onthe rim, the tire is positioned along only a small portion the width ofthe upper bridge. Under these conditions, the quantity of air blown intothe tire by a pump escapes at various points between the sides and theupper bridge, thereby achieving neither inflation, nor any seal.

[0011] This problem also becomes apparent while riding the cycle, if thetire is not adequately pressed against the sides of the rim. In case ofa lateral impact, for example caused by a stone, the air can escape ifthe tire becomes removed from the rim, especially if its pressure islow. Indeed, in such a case, the sides of the tire are no longer pushedup against the rim flanges by the air tube.

SUMMARY OF THE INVENTION

[0012] An object of the invention is to propose an improved rim that isprovided for a tubeless assembly of the tire.

[0013] Another object of the invention is to propose a rim whose contourimproves tire inflation conditions.

[0014] Yet another object is to propose a rim whose contour improves theretention of the tire when it is inflated.

[0015] Other objects and advantages of the invention will becomeapparent from the following description.

[0016] The rim for a bicycle wheel according to the invention has anannular channel along its periphery which is provided to receive thetire, such channel being demarcated by an upper bridge devoid ofopenings with the exception of the valve opening, and two lateralflanges, such flanges having butts designed to grip the tire. The upperbridge has a narrow and recessed rim well demarcated by a base and twolateral walls, the rim well being bordered by two bead seats, at leastpartially inclined, so that the external diameter of the rim in the areaof the bead seats decreases from the well towards the flanges.

[0017] The bicycle wheel according to the invention has a rim such asdefined previously.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention will be better understood with reference to thefollowing description and the annexed drawings that form an integralpart thereof, wherein:

[0019]FIG. 1 shows a side view of an entire wheel equipped with a tire;

[0020]FIG. 2 is a front sectional view of a rim contour according to apreferred embodiment of the invention, in the area of a spoke grippingopening;

[0021]FIG. 3 is a side sectional view of a portion of the rimrepresented in FIG. 2;

[0022]FIGS. 4, 5 and 6 represent a sectional view of the rim equippedwith its tire, and illustrate the various inflation phases of the tire;and

[0023]FIG. 7 is related to an alternative embodiment of the rim.

DETAILED DESCRIPTION OF THE INVENTION

[0024]FIG. 1 represents a wheel 1 that includes, in a known manner, arim 2 connected to a central hub 3 via two sets of spokes. Only the setof spokes 4 is visible in FIG. 1. The spokes are of any appropriatetype, straight or bent, and their arrangement can be either radial orcriss-crossed. In addition, the wheel can be any wheel, be it the frontor the rear wheel.

[0025] In a known manner, the rim is made from a section made of a lightalloy, aluminum or otherwise, that is curved in a circle and whose twoends are preferably assembled together by welding, so as to obtain agood seal in this area.

[0026] The wheel 1 represented in FIG. 1 is also equipped with a tire 5.The tire 5 is a tire having normal dimensions. The dimensions of thetire correspond to those defined by the standard ISO 5775-1 for example.

[0027] In a known manner, such a tire has a central running tread thatis bordered by two lateral sides. The base of the lateral sides, orbead, is thicker and encloses a rigid or flexible rod whose length hasbeen defined. This rod is deformable, and it is made from a metallicwire or from a non-metallic material. At rest, its length is animportant dimension of the tire and it defines the inner diameter of thetire at rest. This diameter is adapted to the nominal diameter of therim, i.e., the diameter of the upper bridge of the rim, when measuredalong the retention flange for the tire, corresponds for example, to thenominal diameter defined by the standard ISO 5775-2. Depending on thetires, the inner diameter can vary within fairly wide tolerances,especially depending on the thickness of the rod and the material thatsurrounds it, such that different tires can be mounted in a more or lesstightened manner on the same rim.

[0028] The invention has been implemented with tires that are currentlyavailable commercially. However, it would be possible to envisionspecial tires designed to equip the rim according to the invention, forexample, by adjusting the inner diameter of the tire by taking intoaccount the contour shape that will be described, or by modifying theinner and/or outer surface of the sides.

[0029] The wheel 1 represented in FIG. 1 also has an inflation valve 6.This valve is preferably of a special type, adapted to the contour ofthe rim and to the tubeless assembly method, but it does not constitutean integral part of the instant invention. Any appropriate valve couldalso suffice.

[0030]FIG. 2 represents the contour of rim 2 according to a preferredembodiment of the invention.

[0031] In a known manner, the rim has an upper bridge 10, a lower bridge11 connected together by two flanks 12 and 13, so as to form a casing.The sides are extended towards the outside by rim flanges 14 and 15 thathave, at their ends, respective butts 16, 17. All these differentelements are known. As shown in FIG. 2, the upper bridge and the flangesform an annular channel adapted to receive the tire.

[0032] The rim 2 has openings for gripping the spokes that are locatedonly in the area of the lower bridge 11. The upper bridge 10 is notbored with openings for the passage or grip of the spokes. As such, FIG.2 represents an opening 18 located on the lower bridge 11. The openingis threaded to enable the screwing of a nipple or an end piece forgripping the spoke, which is also used to adjust the tension of thespoke. These elements are of any appropriate type and will not bedescribed in further detail.

[0033] Preferably, the lower bridge was bored by an extrusion boringtechnique. According to this technique, instead of being cut, thematerial is pushed back so as to form a kind of chimney. This chimneyensures that the bridge is not weakened in this area. It also providesan inner surface that can be threaded easily.

[0034] This boring method is not restrictive, and any method forgripping the spokes could suffice, whether it be at the lower bridge, orfor example, at a rib instead of the lower bridge.

[0035] According to the invention, the upper bridge 10 has, in itsmedian portion, an annular rim well 20. The rim well is recessed withrespect to the surface of the upper bridge and is narrow. It isdemarcated by a base 21 of the rim well oriented parallel to the axis ofthe rim and two lateral walls 22 and 23. On each side of the rim well,the upper bridge has two lateral seats 24, 25 for the tire beads. Thebead seats 24 and 25 also connect the rim well to the two flanges 14 and15 of the rim. The nominal diameter of the rim corresponds to theexternal diameter of the bead seats 24 and 25 at their junction with theflanges 14 and 15.

[0036] The two lateral walls 22 and 23 of the rim well are substantiallyparallel with respect to a radial plane, or as has been represented,slightly converging in the direction of the rim well base. In theembodiment illustrated, the angle of inclination is on the order of 10degrees with respect to a radial plane. Also, the well 20, as defined bythe base 21 and the walls 22, 23, is substantially symmetrical withrespect to a radial plane, as shown in the axial sectional view of FIG.2, for example. In fact, the entire rim is substantially symmetricalwith respect to a radial plane.

[0037] The bead seats 24 and 25 are preferably slightly inclinedobliquely so that their external diameter is maximized and thendecreases from the walls of the rim well towards the flanges 14 and 15.In a cross section, as has been represented, each of the bead seats hasa projecting ridge 24 a, 25 a adjacent to the rim well, and then onepart 24 b, 25 b that is parallel to the axis and provided as a seat forthe beads of the tire. In a variation, the bead seats could have asection with a regular slope from the rim well towards each of the rimflanges.

[0038] As will become clearer in the following discussion, it isimportant that the beads of the tire cross a maximum diameter zonebetween the rim well and their seats along the flange. As an example,good results have been obtained with a difference of 1 mm between thediameter of the bead seat at the edge of the rim well and the diameteragainst the flange. A value of 0.35 mm is also satisfactory. Generally,it can be said that a difference in diameter that is comprised between0.2 and 2 mm suffices. Preferably, the junction between the lateralwalls of the rim well and the bead seats is rounded so as to ensure arelative continuity.

[0039] Thus, contrary to normal rims, the bead seats do not convergetowards the center of the wheel. In fact, the relative distance betweenthe base of the rim well and the peak of the rim flanges is of the sameorder of magnitude as the relative distance between the center of thebridge and the peak of the rim flanges for a traditional rim. However,since the rim well is bordered here with two oblique bead seats, with amaximum diameter zone, the rim well appears to be narrow and recessedwith respect to the contour of a traditional rim.

[0040] The dimensions of the rim 2 are determined in the followingmanner in relation with the diameter of the tire rods.

[0041] The nominal diameter of the rim at the junction between the beadseats 24 and 25 and the flanges 14, 15 is substantially equal to theinner diameter of the tire, or slightly more, so as to cause a slighttightening of the rods against the bridge.

[0042] In a correlative manner, the maximum diameter of the bead seats,at the peaks of the ridges, is greater than the inner diameter of thetire. In fact, this diameter is greater than the nominal diameter of therim.

[0043] The height of the rim flanges 14 and 15 and the shape of thebutts 16 and 17 are determined in the normal manner, so as to obtain agood grip of the tire when it is inflated.

[0044] The width of the rim well 20 is substantially equal to thethickness of both beads 30, 31 of the tire pressed against one another,or in other words, the width is provided such that both beads have justenough space to be housed in the rim well. It is also provided such asto cause a slight pinching of the tire beads against one another so thatonce the tire beads are engaged in the rim well, they tend to becomeseparated naturally from one another and press against the walls of therim well. For example, one can take as the order of magnitude, an innerwidth of the rim well comprised between a half and a third of the bridgewidth measured between the flanges.

[0045] The depth of the rim well 20 has an order of magnitude that isequal or less than the height of the flanges 14 and 15 measured beneaththe butts. This depth is at least enough for the tire to be mountedaccording to the operating method that will be described hereinafter.

[0046] As a non-restrictive example, an all-terrain bicycle wheel hasbeen made with a rim having a nominal diameter of 560 mm, a diameter atthe peak of the flanges of 571 mm, an overall width of approximately 23mm, and a width of approximately 20 mm between the flanges. The diameterat the peak of the ridges of the bead seats is greater than 0.35 mm withrespect to the nominal diameter. The rim well has a width of 7.25 mm anda depth of 3.35 mm. As for the bead seats, they have a width of 7 mm.These values naturally represent only one example of the orders ofmagnitude. To mount the tire on the rim, FIG. 4 shows a sectional viewof the wheel in the area of the valve. According to the embodimentillustrated, the valve 6 is screwed in the lower bridge 11, and it has,at its end, an injection nozzle that crosses the upper bridge 10 at thebase 21 of the rim well 20. The valve 6 thus ends in the base of the rimwell 20. A seal is obtained in this area, by any appropriate means, suchas an O-ring seal.

[0047] The tire is set against the rim and a first side is engaged onthe adjacent rim flange. In light of the dimensions defined previously,the side of the tire can be engaged entirely between the two flanges 14and 15 only if a large portion of its length, at least approximately onehalf thereof, was previously introduced into the rim well 20 in a firstengagement phase of the tire. Over a first part of its length, in therim well 20, the side of the tire molds to the base of the rim wellalong a diameter that is smaller than its inner diameter, such that onthe opposite side, the side of the tire can cross the butt of the flangewhich has a greater diameter.

[0048] Once the rim flange is crossed, the side of the tire isintroduced into the rim well 20 along its entire circumference. It iskept in the rim well due to the fact that the diameter at the peak ofthe walls 22 and 23 of the rim well is slightly greater than the innerdiameter of the tire.

[0049] The second side of the tire is introduced in the same way betweenthe two rim flanges, and as with the first side, it is introduced andkept engaged in the rim well.

[0050]FIG. 4 illustrates this assembly phase, with the two sides 29 and30 of the tire engaged in the rim well 20. The narrowness of the rimwell and the natural elasticity of the tire structure naturally ensurethat the sides are pushed up against the walls 22 and 23 of the rim well20, such that, as can be seen in FIG. 4, they come naturally intocontact with the walls 22 and 23. In order to improve the seal betweenthe sides of the tire and the walls 22 and 23 of the rim well, one couldprovide, on the external surfaces of the tire sides, towards the beads,a small circular projecting lip. In the area of the beads, provisioncould be made for nipples or other projecting elements which would actas spacers between the two beads during this assembly phase. Thesenipples reinforce the support of the tire sides against the walls of therim well as well as the seal in this area.

[0051] As is visible from FIG. 4, the valve 6 ends in the area of thejunction between the two beads, and if such is the case, of the aperturethat exists between them.

[0052] As has been described previously, the sides of the tire takesupport against the walls 22 and 23 of the rim well. The supportpressure against the rim well is not much, but it is enough for the airblown through the valve 6, even under low pressure, to remain in thevolume demarcated by the rim well and the tire beads, and then enter theinner volume of the tire, expand its outer envelope, and progressivelyincrease the inner pressure of the tire. This also increases the contactpressure of the sides of the tire against the walls of the rim well andprogressively reinforces the seal in this area.

[0053]FIG. 5 illustrates this first primary inflation phase of the tire.It must be emphasized that when this first phase begins, there alreadyexists a relative seal between the beads of the tire and the rim well,and then, during this primary phase, the two beads 31, 32 at the base ofthe sides remain in the rim well, and the seal of the tire takes placebetween the sides 29 and 30 of the tire and the walls 22 and 23 of therim well.

[0054] As inflation continues, the pressure inside the tire increases,and the structure of the tire subjects the rods to relatively highradial stresses, which cause the rods to be slightly distended. After acertain pressure threshold is exceeded, the extension of the rodsbecomes enough for the sides of the tire to cross the ridges 24 a and 25a of the bead seats, and be positioned against the rim flanges 14 and 15and their butt 16 and 17, due to the effect of the inner pressure of thetire. Generally, the two sides cross their respective ridges 24 a, 25 anot simultaneously, but one after another. Once the tire has beenpositioned, all that one has to do is adjust the inner pressure to thedesired pressure. Generally, it is necessary to lower the pressure. FIG.6 illustrates the tire in this final assembly phase, i.e., in a finaltire mounted position.

[0055] The tire is thus kept in position against the flanges of the rim.A seal is obtained between the beads of the tire and the upper bridge ofthe rim. In light of the relatively malleable material of the tire, ithas natural sealing capacity in this area. If necessary, the tiresurface in this area can be made such that the seal is reinforced evenfurther. Also, with this objective in mind, one preferably uses a tirewith an inner diameter that is slightly less than the nominal diameterof the rim, so as to promote the tightening of the tire beads on thebridge of the rim.

[0056] In case of a lateral impact, it has been noted that the side ofthe tire could become dissociated at places from the butt of the flange,whereas for normal impacts, the bead of the tire remained pressedagainst the flange. The inclination of the bead seats contributes to theretention of the beads 31, 32 of the tire against the flanges. In theseconditions, the tire reassumes its shape without any loss of pressure assoon as the impact is over.

[0057] In light of the preceding, one can see that the narrow andrecessed central rim well is useful for the engagement of the two sidesof the tire. In addition, its walls are useful in ensuring a seal forthe tire during the primary inflation phase. The inclination orobliqueness of the bead seats is useful in allowing the sides to beretained in the rim well during the entire primary inflation phase. Itis also useful, once the tire has been inflated, in the retention of thebeads of the tire in case of a lateral impact.

[0058] The deflation of the tire is done according to the reverse of theoperating method described previously. First, the tire is deflated,either by opening the valve or by disassembling it. Thereafter, oneafter the other, the sides of the tire are brought into the rim well soas to be able to progressively cross the flanges, if necessary, with thehelp of an appropriate tool, for example, a tire dismantling tool.

[0059]FIG. 7 illustrates an alternative embodiment of the rim accordingto the invention. According to this variation, a strip of soft material,such as a foam 35 is added to the base of the rim well 34 so as to fillup the base of the rim well. The rim well 34 is deeper than the previousrim well 20, by a height that generally corresponds to the thickness ofthe strip 35. The thickness of the foam is enough so that the diameterof the rim, when measured at the upper surface of the foam, is greaterthan the inner diameter of the tire. This foam strip is used in thefirst phase of the tire assembly. Its aim is to ensure a relative sealbetween the beads of the tire and the base of the rim well, at least atthe start of the primary inflation phase, and not between the sides andthe lateral walls of the rim well. This could be, for example, a lightfoam with closed cells, preferably having a smooth external surface.When the tire is mounted, during their engagement in the rim well, thebeads become seated in the foam strip which becomes slightly deformed,on the one hand, to allow the complete engagement of the tire, and onthe other hand, to be adapted to the inner diameter of the beads, oncethe sides of the tire are engaged in the rim well.

[0060] The valve ends in the inner volume of the tire. The inflationtechnique is the same as the one described previously. During theinitial priming, air is captured between the envelope of the tire andthe upper surface of the foam.

[0061] After the initial inflation priming is over, the beads of thetire become separated, and take support against the walls of the rimwell, as has been described previously. Then, the rods are deformed andthe beads are installed on the seats, after crossing the ridges, or asthe case may be, the maximum diameter zone.

[0062] Advantageously, with this variation, the rim well can be wider,and indeed, it is no longer necessary to elastically pinch the two sidesbetween the edges of the rim well for the primary inflation to begin,because the initial seal occurs between the bead and the upper surfaceof the foam. In addition, in view of the width-wise elasticity of thefoam, the manufacturing tolerances for the tire can be broader.

[0063] Materials other than foam could be used to cover the rim base, aslong as it forms a strip that increases the perimeter of the rim baseand as long as its upper surface is deformable.

[0064] The present description has been provided only as an example, andone could adopt variations thereof without leaving the scope of theinvention. These variations could be especially related to the spokegrips and the inner shape of the rim flanges and hooks. For example, theflanges could have lips or other projecting contours so as to improvethe grip of the tire. Other variations are also possible.

[0065] In addition, the invention is also related to the so-called hookrims. These rims are different from the butt rims in the shape of theupper bridge and the shape of the flanges that retain the tire. In orderto apply the invention to these rims, one would only have to replace theupper bridge by a bridge having a less hollow overall shape, and whichhas a central rim well and two lateral bead seats with a ridge or othersimilar element along the rim well, with a diameter that was greaterthan the theoretical inner diameter of the tire, so as to retain thetire in the rim well during the entire primary inflation phase.

[0066] Finally, it is to be understood that the invention alsoencompasses a wheel having a rim as described, connected to a hub viaspokes, as well as a complete wheel equipped with a tire mounted in themanner described hereinabove.

What is claimed is:
 1. A tubeless tire-engaging structure for a bicyclewheel, said structure comprising: an annular channel forming an outerperiphery of the wheel, said annular channel comprising a bridge and twolateral flanges, said bridge having a recessed central well, saidcentral well comprising a base and two lateral walls, said well having awidth to facilitate engagement and retention of a pair of tire beadswithin said well, whereby the pair of tire beads touch each other atleast before a primary tire inflation phase to facilitate inflation ofthe tire, said annular channel further comprising seats for the tirebeads during a subsequent tire inflation phase on opposed lateral sidesof said well between said well and respective ones of said flanges, saidbead seats extending obliquely from an edge of said well towardsrespective ones of said flanges, and said bead seats having, adjacentsaid well, a maximum diameter zone, said maximum diameter zone beinggreater than a diameter of said bead seats adjacent said flanges.
 2. Atubeless tire-engaging structure for a bicycle wheel as defined by claim1 , wherein each of said bead seats comprises a ridge adjacent saidwell, and each of said bead seats further includes a portion extendingtowards a respective one of said flanges and parallel to a central axisdefined by the annular channel.
 3. A tubeless tire-engaging structurefor a bicycle wheel as defined by claim 1 , wherein said maximumdiameter zone of said bead seats adjacent said well is greater than saiddiameter of said bead seats adjacent said flanges by a value of between0.2 and 2 mm.
 4. A tubeless tire-engaging structure for a bicycle wheelas defined by claim 1 , wherein said width of said well is between athird and a half of the width of the bridge measured between saidflanges.
 5. A tubeless tire-engaging structure for a bicycle wheel asdefined by claim 1 , wherein said lateral walls of said well areinclined by approximately 10 degrees with respect to a radial plane ofsaid annular channel.
 6. A tubeless tire-engaging structure for abicycle wheel as defined by claim 1 , wherein said base of said well isequipped with a strip of foam having a smooth upper surface and beingelastically deformable.
 7. A tubeless tire-engaging structure for abicycle wheel as defined by claim 1 , wherein said structure comprises arim for a bicycle wheel.
 8. A tubeless tire-engaging structure for abicycle wheel as defined by claim 7 in combination with a central huband a plurality of spokes connecting said central hub to said rim,thereby forming a bicycle wheel.
 9. A tubeless tire-engaging rim for abicycle wheel, said rim comprising: a lower bridge, an upper bridge,lateral sides extending between said lower bridge and said upper bridge,said lateral sides extending radially outwardly beyond said upper bridgeto form lateral flanges, the tire to be retained between said lateralflanges; said upper bridge having a rim well recessed in a centralportion of said upper bridge between said lateral flanges, said rim wellcomprising a base and a pair of lateral walls extending from said base,said well having a predeterminately sized width to facilitatepositioning a pair of tire beads of a tubeless tire in mutual contactwithin said well before a primary tire inflation phase to facilitateinflation of the tire; said upper bridge further comprising laterallyopposed bead seats for seating the pair of tire beads, said upper bridgefurther comprising laterally opposed ridges, each of said ridges beingpositioned between a respective one of said bead seats and a respectiveone of said lateral walls of said rim well, said ridges comprising azone of said upper bridge having a greater diameter than a diameter ofsaid bead seats.
 10. A rim according to claim 9 , wherein said lateralflanges are substantially parallel with respect to a radial plane.
 11. Arim according to claim 9 , wherein said lateral walls slightly convergetoward said base of said well.
 12. A rim according to claim 11 , whereinsaid laterals walls converge at an angle of about 10° with respect to aradial plane.
 13. A rim according to claim 9 , wherein said upper bridgeis substantially symmetrical with respect to a radial plane.
 14. A rimaccording to claim 9 , wherein the rim is substantially symmetrical withrespect to a radial plane.
 15. A rim according to claim 9 , wherein saidbead seats of said upper bridge extend substantially parallel to an axisdefined by the rim.
 16. A rim according to claim 9 , wherein said ridgeshave a maximum diameter zone greater than a diameter of said bead seatsby a value between 0.2 and 2.0 millimeters.
 17. A rim according to claim9 , wherein said width of said well is between one-third and one-half ofthe width of said upper bridge measured between said flanges.
 18. A rimaccording to claim 9 , wherein a strip of elastically deformable foammaterial is positioned on said base of said well, said strip having asmooth upper surface.
 19. A rim according to claim 9 in combination witha central hub and a plurality of spokes connecting said central hub tosaid rim, thereby forming a bicycle wheel.
 20. A tubeless tire-engagingstructure for a bicycle wheel, said structure comprising: an annularchannel forming an outer periphery of the wheel, said annular channelcomprising a bridge and two lateral flanges, said bridge having arecessed central well, said central well comprising a base and twolateral walls, said well having a width to facilitate receiving a pairof tire beads within said well, a strip of soft material positionedwithin said well for engagement with said pair of tire beads within saidwell before a primary tire inflation phase to facilitate inflation ofthe tire, said annular channel further comprising seats for the tirebeads during a subsequent tire inflation phase on opposed lateral sidesof said well between said well and respective ones of said flanges, saidbead seats extending obliquely from an edge of said well towardsrespective ones of said flanges, and said bead seats having, adjacentsaid well, a maximum diameter zone, said maximum diameter zone beinggreater than a diameter of said bead seats adjacent said flanges.
 21. Atubeless tire-engaging structure for a bicycle wheel as defined by claim20 , wherein said strip of soft material comprises an elasticallydeformable material.
 22. A tubeless tire-engaging structure for abicycle wheel as defined by claim 21 , wherein said elasticallydeformable material comprises a foam having a smooth upper surface.